Potential energy surface sensor chip and use of potential energy surfaces on a sensor chip and method for preventing a sensor chip from being soiled

ABSTRACT

In a sensor chip according to the existing art, contaminants in the medium flowing past the sensor chip result in deposits in the sensor region.  
     A sensor chip ( 1 ) according to the present invention has, at least upstream from the sensor region ( 17 ), at least one potential surface ( 44, 47, 50, 53 ) that, by electrical interaction with the contaminants in the flowing medium, prevents precipitation in the sensor region ( 17 ).

BACKGROUND INFORMATION

[0001] The invention proceeds from a sensor chip having potentialsurfaces, and from a use of a potential surface on a sensor chip, andfrom a method for avoiding contaminants on a sensor, according to thespecies defined in claims 1, 13, and 14 and 15, respectively.

[0002] DE 196 01 791 A1 has disclosed a sensor chip having a sensorregion that is made up, for example, of a frame element, a recess, and amembrane that forms a sensor region. Contaminants, for example oil, towhich the sensor chip is exposed can at any time result in anundesirable influence on the measured signal of the sensor chip in thevicinity of the sensor region. Contamination with oil of the sensorregion, or in the immediate vicinity around the sensor region, modifiesthe thermal conductivity on the surface of the sensor chip and thus hasa distorting effect on the measured signal. In addition, oil depositedon the sensor chip serves as an adhesion promoter for solid particlescontained in a flowing medium. These captured particles in turnadditionally enhance the unfavorable influence.

[0003] U.S. Pat. No. 5,705,745 describes a sensor chip having a membraneon which temperature resistors and heating resistors are positioned, themembrane being surrounded by a thermal conduction element that can alsobe U-shaped. The thermal conduction element is not heated, i.e. it hasno potential.

[0004] U.S. Pat. No. 4,888,988 describes a sensor chip having amembrane, a metallic conductor being positioned around the membrane.This conductor is the common neutral conductor of a measurementassemblage on the sensor chip for a measurement method.

[0005] DE 198 01 484 A1 describes a sensor chip having a membrane,electrical conductors through which an electrical current flows beingpositioned around the membrane. These conductor paths are temperaturesensors that are used for the measurement method or measurementprocedure.

[0006] DE 29 00 210 A1 and U.S. Pat. No. 4,294,114 describe a sensorchip that has a temperature-dependent resistor on a support, a furtherresistor that heats the substrate being mounted on the support.

[0007] DE 42 19 454 A1 and U.S. Pat. No. 5,404,753 describe a sensorchip that has a reference temperature sensor at a distance from a sensorregion.

[0008] DE 31 35 793 A1 and U.S. Pat. No. 4,468,963 describe a sensorchip that has, upstream and/or downstream from the sensor resistor, afurther resistor that, however, influences the measured signal.

ADVANTAGES OF THE INVENTION

[0009] The sensor chip according to the present invention having thepotential surfaces and the use according to the present invention ofpotential surfaces on a sensor chip and the method according to thepresent invention for avoiding contaminants on a sensor chip, having thecharacterizing features of claims 1, 13, and 14 and 15, respectively,have, in contrast, the advantage that contamination of the sensor chipis reduced or prevented in a simple fashion.

[0010] The actions set forth in the dependent claims make possibleadvantageous developments of and improvements to the sensor chip recitedin claim 1.

[0011] Advantageously, potential surfaces that protect the sensor regione.g. in the event of backflows are also positioned downstream from thesensor region.

[0012] An advantageous potential drop is achieved by way of a positivepotential on a first potential surface and a negative potential on asubsequent potential surface.

[0013] The potential surfaces advantageously have a U-shape whichadvantageously surrounds the sensor region.

[0014] The potential surfaces are advantageously embodied, like theheating resistors, as a conductor path, since this is a known and simplemanufacturing method.

[0015] The sensor region is advantageously operated independently of thepotential surfaces, i.e. the measurement or the measured signal suppliedby the sensor region is not influenced by operation of the potentialsurfaces, and vice versa.

DRAWING

[0016] Exemplary embodiments of the present invention are depicted insimplified fashion in the drawings, and explained in more detail in thedescription below. In the drawings:

[0017]FIG. 1 shows a sensor chip according to the existing art;

[0018]FIG. 2a shows a first, FIG. 2b a second, and FIG. 2c a thirdexemplified embodiment of a sensor chip according to the presentinvention.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

[0019]FIG. 1 shows a sensor chip according to the existing art that isimproved according to the present invention in accordance with theremarks referring to FIGS. 2a through 2 c. The manufacturing method andapplication of such a sensor chip are described in more detail in DE 19601 791 A1, the content of which is explicitly intended to be part ofthis disclosure.

[0020] The sensor chip has a frame element 3 that is made, for example,of silicon. Frame element 3 has a recess 5. Mounted on the frame elementis, for example, a dielectric layer 21 made e.g. of SiO₂. Layer 21 canextend over the entire frame element 3, but also over only a region ofrecess 5. This region constitutes a membrane 33 that partially orentirely delimits recess 5 on one side. Mounted on the side of membrane33 facing away from recess 5 are at least one, for example three, metalpaths 19. Metal paths 19 constitute e.g. electrical heaters and/ormeasurement resistors, and with membrane 33 constitute a sensor region17. At least sensor region 17 is preferably covered with a protectivelayer 23. Protective layer 23 can also extend only over metal paths 19.

[0021] The sensor chip has a surface 27 that is in direct contact with aflowing medium.

[0022]FIG. 2a shows, in a plan view, a first exemplary embodiment of asensor chip 1 configured in accordance with the present invention.

[0023] Positioned on sensor region 17 are e.g. metal paths that, forexample, constitute at least one electrical heating resistor 35 and atleast one temperature sensor 37. Temperature sensor 37 is e.g. also anelectrical resistor. In this case there are two temperature sensors 37and one temperature resistor 35 which are positioned predominantlyparallel to one another, temperature sensors 37 running to the left andright of heating resistor 35. The metal paths are positioned for themost part in sensor region 17 and are the prerequisite for a measurementmethod for determining the at least one parameter, for example thetemperature and/or flow volume, of the flowing medium. Sensor region 17is therefore connected to a known monitoring and control circuit (notdepicted). Sensor region 17 can be constituted, for example, by membrane33 described above.

[0024] Sensor chip 1 is positioned in a flowing medium for determinationof at least one parameter, the flowing medium flowing, in a main flowdirection 42, past or over sensor chip 1 and surface 27. The flowingmedium can contain impurities that result in contamination of sensorchip 1. These are e.g. oil, or salts dissolved in water. In order toavoid or reduce contamination, a first 44 and a second 47 potentialsurface are positioned in front of sensor region 17 in main flowdirection 42. First potential surface 44 has, for example, a positivepotential of 1 volt that derives e.g. from a voltage source independentof the monitoring and control circuit. Second potential surface 47 hasno potential or a negative potential. The potential drop can be of anymagnitude, and can also be configured in reverse.

[0025] The electrical interaction of the potential surfaces with theliquid and contaminant particles that are contained in the flowingmedium results in a prevention of deposition in sensor region 17, sincethe contaminant particles are repelled by the electric field of theapplied voltage and thus deflected around sensor region 17. This happenswhen the potential of the potential surfaces and the charge of theliquid and contaminant particles are similarly charged, i.e. either bothpositive or both negative.

[0026] If the potential of the potential surfaces and the charge of theliquid and contaminant particles are opposite, i.e. the potential ispositive and the liquid and contaminant particles negative, or viceversa, the liquid and contaminant particles are attracted to surface 27and are intentionally deposited in the region of the potential surfaces,but not in sensor region 17. Electrostatic fields are preferably used.Alternating fields can, however, also be applied.

[0027]FIG. 2b shows a second exemplary embodiment of a sensor chip 1embodied according to the present invention. Sensor chip 1 additionallyhas, downstream in sensor region 17, a third 50 and a fourth 53potential surface. First potential surface 44 is e.g. at the samepotential as fourth potential surface 53, and second 47 and third 50potential surface also have, for example, the same potential.Contamination in sensor region 17 is thus also avoided in the presenceof backflows, for example due to pulsations, that may occur opposite tomain flow direction 42. Potential surfaces 44, 47, 50, 53 upstream anddownstream of sensor region 17 do not necessarily need to have anidentical potential difference.

[0028]FIG. 2c shows a third exemplary embodiment of a sensor chip 1embodied according to the present invention. Potential surfaces 44, 47,50,53 each constitute parts of a U-shape that at least partiallysurrounds sensor region 17. Proceeding from FIG. 2b, therefore, secondand third potential surfaces 47, 50 are connected to one another, andfirst potential surface 44 to fourth potential surface 53, which thenconstitute one potential surface.

[0029] The following description furthermore applies to all theexemplified embodiments.

[0030] Sensor chip 1 is, for example, of plate-shaped configuration andhas surface 27 past which the flowing medium flows. Sensor region 17 andpotential surfaces 44, 47,50, 53 are arranged, for example, together onsurface 27.

[0031] Potential surfaces 44, 47, 50, 53 are, for example, embodied insuch a way that they have a length, at least upstream or downstream fromsensor region 17, which is longer than a length 1 of sensor region 17transverse to main flow direction 42. Sensor region 17 is therebyprotected from contamination over its entire length 1.

[0032] Resistors 35, 37 and/or potential surfaces 44, 47, 50, 53 arepreferably embodied as conductor paths.

[0033] Potential surfaces 44, 47, 50, 53 can be positioned entirely orpartially on sensor region 17, directly adjacent to sensor region 17 orat a distance from sensor region 17.

[0034] Sensor region 17 can be operated independently of potentialsurfaces 44, 47, 50, 53, i.e. the measurement or measured signal thatsensor region 17 supplies is not influenced by the operation ofpotential surfaces 44, 47, 50, 53. The monitoring and control circuit ofsensor region 17 can send signals to potential surfaces 44, 47, 50, 53,for example can apply a specific voltage or switch off a voltage, butpotential surfaces 44, 47, 50, 53 are not part of the measurement orcontrol loop of sensor region 17. The magnitude of the applied voltagecan be varied.

[0035] The potential of potential surfaces 44, 47, 50, 53 can also bedefined already at the design stage, so that no control circuit isrequired for them in order to establish a specific potential, which isthen defined for the entire service life of the sensor chip.

What is claimed is:
 1. A sensor chip for measuring at least oneparameter of a flowing medium, which has a sensor region for at leastone measurement method, the medium having a main flow direction (42),wherein at least one potential surface (44, 47, 50, 53) is positioned atleast partially upstream in front of the sensor region (17) on thesensor chip (1).
 2. The sensor chip as recited in claim 1, wherein atleast one further potential surface (44, 47, 50, 53) is positioneddownstream behind the sensor region (17) on the sensor chip (1).
 3. Thesensor chip as recited in claim 1 or 2, wherein the at least onepotential surface (44, 4, 50, 53) is positioned at a distance from thesensor region (17).
 4. The sensor chip as recited in claim 1 or 2,wherein one potential surface (44, 47, 50, 53) has a positive electricalpotential and another directly adjacent potential surface (44, 47, 50,53) has no potential or a negative potential, the two potential surfaces(44, 47, 50, 53) being positioned in front of or behind the sensorregion (17) in the main flow direction (42).
 5. The sensor chip asrecited in claim 1, wherein the potential surface (44, 47, 50, 53) has aU-shape.
 6. The sensor chip as recited in claim 1, wherein the sensorregion (17) has a membrane (33).
 7. The sensor chip as recited in claim1, wherein at least one heating resistor (35) and at least onetemperature sensor (37), which (35, 37) are positioned for the most partin the sensor region (17), are positioned in the sensor region (17). 8.The sensor chip as recited in claim 1, wherein the sensor region (17)has a length (1) transverse to the main flow direction (42); and thepotential surface (44, 47, 50, 53) is positioned transversely to themain flow direction (42) and is longer than the length (1).
 9. Thesensor chip as recited in claim 7, wherein the resistors (35) or thetemperature sensor (37) are embodied as conductor paths.
 10. The sensorchip as recited in claim 1 or 2, wherein the potential surface (44, 47,50, 53) is embodied as a conductor path.
 11. The sensor chip as recitedin claim 1, wherein the sensor chip (1) has at least one surface (27)past which the flowing medium flows; and the sensor region (17) and thepotential surface (44, 47, 50, 53) are positioned together on onesurface (27).
 12. The sensor chip as recited in claim 1, wherein thesensor region (17) is electrically operated independently of thepotential surfaces (44, 47, 50, 53).
 13. Use of at least one potentialsurface (44, 47, 50, 53) to deflect entrained particles of a flowingmedium in the vicinity of the sensor region (17) using electric fields,the potential surface (44, 47, 50, 53) being positioned on a sensor chip(1) which is used for determining at least one parameter of the flowingmedium.
 14. A method for avoiding contamination on a sensor chip (1)that has a sensor region (17) and is positioned in a flowing medium,wherein at least one potential surface (44, 47, 50, 53) generates, byway of an applied electrical voltage, an electric field that deflectsentrained particles of the medium around the sensor region (17).
 15. Amethod for avoiding contamination on a sensor chip (1) that has a sensorregion (17) and is arranged in a flowing medium, wherein at least onepotential surface (44, 47, 50, 53) generates, by way of an appliedelectrical voltage, an electric field that attracts entrained particlesof the medium upstream or downstream from the sensor region (17) in theregion of the potential surfaces (44, 47, 50, 53).